TIKRIT, Iraq (AP)  A roadside bomb killed two American soldiers and wounded three others in Saddam Hussein's hometown Saturday, and U.S. forces responded by making several arrests and dispatching troops into the streets in a show of force.

The slain soldiers were the first casualties suffered by the 1st Infantry Division's 1st Battalion, 18th Infantry Regiment, which took over control of the restive Sunni Triangle town of Tikrit on Saturday.

The soldiers, based in Germany, have been in Iraq for less than a month and formally took over security duties in the Tikrit area several hours after the fatal 5 a.m. blast.

In Baghdad, a bomb planted in a shop killed Haidar al-Qazwini, brother-in-law of a Shiite member of the U.S.-appointed Iraqi Governing Council, Ibrahim al-Jaafari, an aide to al-Jaafari said.

Iraqi police Capt. Abbas Nima said an unidentified man entered the shop and left a bag containing explosives, which later detonated.

Also Saturday, the White House said it sent a senior official to Baghdad to help form an interim government — action that is needed before sovereignty can be transferred to the Iraqi people by June 30.

In Baghdad, coalition spokesman Dan Senor identified the official as Robert Blackwill of the National Security Council staff, who visits Iraq every four to six weeks.

Blackwell was sent in part to resolve problems some Shiite members of the Governing Council have with the interim constitution signed by the council Monday, a senior administration official said. He also is charged with convincing the Governing Council to let the United Nations help set up elections, which are scheduled to be held before Dec. 31.

In the Tikrit attack, gunshots were heard near the rear vehicle in a three-Humvee American patrol seconds before a remote-controlled bomb, which included an artillery shell, exploded under the second car, Capt. Tim Crowe told The Associated Press. There were conflicting reports about the source of the gunfire.

Roadside bombs have become the main threat to U.S. soldiers on patrol in the Sunni Triangle, a region north and west of Baghdad that has seen some of the fiercest guerrilla attacks.

Saturday's deaths brought to 560 the number of U.S. service members who have died since the beginning of military operations in Iraq, according to the Department of Defense. Of those, 381 died as a result of hostile action and 179 died of non-hostile causes, the department said.

One soldier at the scene said the bomb blast destroyed the vehicle and left a large crater in the road. Two soldiers in the car were killed, while another three were wounded and taken to a military hospital north of Tikrit in stable condition, Army spokeswoman Maj. Debra Stewart said.

Minutes after the attack, a Bradley fighting vehicle sped to the scene and strafed the area where shooting was heard with a heavy machine gun. It was unclear whether there were any casualties.

About 100 heavily armed soldiers poured out of the main U.S. military base in Tikrit, searching for evidence and quizzing locals for information about the attack.

"We have arrested several people and continue to question them," Crowe said. "We believe they may have been connected with what happened."

He did not elaborate.

But he said the 1st Infantry Division, aided by Iraqi police and the Iraqi Civil Defense Corps, would have an "increased presence" in Tikrit in response to the attack.

The U.S. military in Iraq is about halfway through the biggest troop rotation in its history, pulling out 130,000 troops — some of whom have been here since the March 2003 invasion of Iraq.

Soldiers on the front line facing the anti-U.S. insurgency — believed led by Saddam loyalists and Islamic militants — have been carrying out joint patrols with the newcomers, trying to acquaint them with the landscape. Saturday was only the second day that troops from the 18th Regiment patrolled alone.

Some 700 soldiers from the 18th Regiment arrived in Tikrit within the last month to replace a similar number from the outgoing unit, which has been patrolling the city, 85 miles north of Baghdad, since it fell to U.S. forces in April.

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